Well, I stopped by the Mercedes service center that is pretty close to my house - about 10 minutes away, luckily - and picked up 2 gallons of MB coolant! Hurray for me!! 22$ per gallon isn't too expensive, especially considering you don't have to change it THAT often. I will take it to my mechanic and have him drain the 'green stuff' his assistant put in there, flush it out, and refill with the MB coolant.

Now, the stuff from MB needs to be diluted 50/50 with distilled water, right? I'd like to know for sure so I can be non-ignorant when I go in early next week!

Thanks!